Embodiments of the invention relate to elevator systems, and more particularly, to a load bearing member having a high bending stiffness configured for use in an elevator system.
Elevator systems are useful for carrying passengers, cargo, or both, between various levels in a building. Some elevators are traction based and utilize load bearing tension members such as ropes or belts for supporting the elevator car and achieving the desired movement and positioning of the elevator car.
Where ropes are used as tension members, each individual rope is not only a traction device for transmitting the pulling forces but also participates directly in the transmission of the traction forces. Where belts are used as a tension member, a plurality of adjacent ropes configured as tension members are embedded in a common elastomer belt body. The tension members are exclusively responsible for transmitting the pulling forces, while the elastomer material transmits the traction forces. The belt as a traction device, especially the elastomer region between the tension members and the contact surface, is thus exposed to high shear and shearing stresses during operation.
Due to their light weight and high strength, load bearing traction members formed from unidirectional fibers arranged in a rigid matrix composite provide significant benefits when used in elevator systems, particularly high rise systems. However, the unidirectional composite construction results in a high bending stiffness which can produce substantial bending stress when used in an elevator system where the load bearing member is wrapped around a traction sheave. While the bending stresses may be reduced by decreasing the thickness of the load bearing member, the width must be increased to achieve a load bearing member having the same load carrying capacity. As a result of the space constraints for most elevators systems, such an increase in the width of the load bearing members may exceed the space available for the drive machine within the hoistway.